1. Technical Field
The present application relates to a control system for a lawnmower vehicle.
2. Related Art
With regard to the present invention relating to the first aspect and the second aspect, an apparatus for mowing grass such as lawn grass that is planted on the ground surface of a garden or the like is generally referred to as a “lawnmower”, although naturally such apparatuses are also used to mow grasses other than lawn grass. Types of lawnmowers include handheld lawnmowers and wheel movement-type lawnmowers. A handheld lawnmower is a lawn mowing tool comprising a blade for mowing a lawn or the like which an operator carries in their hands in order to mow a lawn while walking around a garden or the like. A wheel movement-type lawnmower is a device that can move over the surface of a garden or the like using wheels. The kinds of wheel movement-type lawnmowers include a lawnmower that an operator moves around a garden or the like while pushing the lawnmower by hand. This type of lawnmower is generally referred to as a “walk behind lawnmower”. A still larger kind of lawnmower apparatus is one in which a lawnmower rotary tool is mounted on a vehicle capable of self-powered travel. In this case, an operator rides on the vehicle and performs traveling and cutting operations. These apparatuses can be referred to as “riding lawnmowers”.
Although a riding lawnmower is a type of vehicle, it is generally not used to travel on roads and is used almost exclusively for so-called “off-road” usage in a garden or the like. A riding lawnmower moves over the surface of ground for lawn mowing work and has a driving source mounted thereon for driving the wheels and driving a lawnmower rotary tool. Commonly, an internal combustion engine, an oil hydraulic motor driven by an internal combustion engine, an electric motor or the like is used as a driving source.
For example, Japanese patent publication No. 2006-507789 discloses a hybrid power apparatus that has mounted thereon a device that integrates an engine and an electricity generator which connects a rotor to an engine shaft of an internal combustion engine. In a lawnmower that is exemplified as a power apparatus, respectively independent electric motors are linked to a plurality of drive wheels so that each drive wheel can be controlled at independently variable speeds. It is noted that as a result, starting, stopping, speed changing, direction changing, and turning of the lawnmower can be smoothly performed. As an example of turning executed by independent speed changes of the drive wheels, an apparatus is mentioned in which both the left and right rear wheels are linked with respective electric motors.
U.S. Pat. No. 7,017,327 B2 discloses, as a hybrid lawnmower, a configuration in which electric power produced by an alternator connected to an engine disposed at the front is used to drive a deck motor for lawnmower blade driving, left and right wheel motors for driving independently-controlled left and right rear wheels, and steering motors that steer left and right front wheels over a range of approximately 180 degrees around an axle. In this case, to turn the lawnmower, the speed difference between the left and right rear wheels is calculated based on input from a steering control section to control the wheel motors, and a steering signal is supplied to the steering motors to control the positions of the left and right front wheels. It is note that, as a result, the lawnmower can be turned without steering the left and right rear wheels. In this connection, it is described as a feature of this configuration that, because the left and right wheel motors are provided inside the rims of the left and right wheels and there is no differential gear mechanism, a space can be secured between the left and right wheels under the frame in which tilting chute that conveys cut grass can be disposed.
Regarding the first invention, as a method for executing a turn in a riding lawnmower, Japanese Patent Publication No. 2006-507789 discloses a method in which the rotational speed of the left rear wheel and the rotational speed of the right rear wheel are caused to differ by electric motors that are independently provided in the left and right rear wheels, respectively. Further, U.S. Pat. No. 7,017,327 B2 discloses applying a speed difference to the left and right rear wheels using left and right wheel motors and controlling the positions of the left and right front wheels with steering motors to execute steering.
In lawn mowing work, there are cases in which some degree of traveling driving force is necessary depending on the state of the ground surface such as the garden surface or the like. For example, when the ground surface is uneven or when the surface is sloped, there are cases when the traveling driving force of the left and right rear wheels as main drive wheels is insufficient. Although the related art as disclosed in Japanese Patent Publication No. 2006-507789 and U.S. Pat. No. 7,017,327 B2 mention a riding lawnmower of a four-wheel type or a three-wheel type a having a front wheel or wheels, in both of these apparatuses a driving source for traveling driving is not connected to the front wheel(s). A steering motor described in U.S. Pat. No. 7,017,327 B2 is a motor for steering the front wheels, that is, a motor for changing the steering angle of the front wheels, and is not a motor that applies a traveling driving force to the front wheels. Thus, in a riding lawnmower according to the related art, depending on the ground surface conditions such as a sloping surface, a case may arise in which the traveling driving force is insufficient.
According to the related art, because the front wheels can freely roll over the ground surface because a traveling driving force is not applied to the front wheels, there are few problems with respect to turning when traveling over a flat surface. In contrast, however, in the case of turning while traveling over a sloping surface, if the aforementioned traveling driving force is insufficient, a case may arise in which the rear wheels and the front wheels slip with respect to the ground surface and the turn itself can not be executed adequately. Further, if a turn is executed while slipping on the ground surface, there is a risk that the planting condition of the lawn or the ground surface state will be damaged.
Even when it can be assumed that a traveling driving force is applied to the front wheels to drive the front wheels and rear wheels at a uniform speed, for example, when executing a turn, a difference will arise between the turning speed of the front wheels and the turning speed of the rear wheels due to the turn center position, and it will not be possible to turn smoothly. As a result of the turn not being performed smoothly, there is a risk that the front wheels or the rear wheels will slip on the lawn and damage the planting condition of the lawn or the ground surface condition. This situation is particularly likely to occur when traveling on a sloping surface. Accordingly, it is necessary to give consideration to executing suitable control between the rotational speeds of the rear wheels and the rotational speeds of the front wheels when turning.
With regard to the second aspect, as a method for executing a turn in a riding lawnmower, Japanese Patent Publication No. 2006-507789 discloses a method in which the rotational speed of the left rear wheel and the rotational speed of the right rear wheel are caused to differ by electric motors that are independently provided in the left and right rear wheels, respectively. Further, U.S. Pat. No. 7,017,327 B2 additionally discloses applying a speed difference to the left and right rear wheels using left and right wheel motors and controlling the positions of the left and right front wheels with steering motors to perform steering.
In lawn mowing work, depending on the level of skill of the operator or the state of the ground surface such as the garden surface or the like, there are cases when particular care is required when traveling or turning. For example, when performing a turning maneuver, although in the case of a skilled operator the turning maneuver can be freely executed even under a comparatively fast traveling speed, in the case of a novice operator in some cases lowering the traveling speed is necessary to correctly execute the turning maneuver. Further, when the turning radius is small there are cases in which the turn is executed using a wheel on one side as the turn center position. However, depending on the state of the wheel on one side, the planting condition of the lawn may be damaged by the turning of the wheel on one side as the turn center position. Further, on sloping ground, if the turning radius is too small the vehicle itself may enter an unstable state due to a shift in the center of gravity of the riding lawnmower.
Thus, depending on the nature of the lawn mowing task, there are times when delicate control is required when traveling or turning. This type of delicate control is not adequately provided for according to the related art.
Regarding a third aspect, as lawnmower vehicles that comprise a lawnmower, a walk behind lawnmower vehicle which a person operates from the rear and a riding lawnmower which a person rides and operates are known. With respect to riding lawnmowers, a riding lawnmower is also known that comprises two main drive wheels and a caster wheel as a steering control wheel, in which the two main drive wheels are driven by a traction power source such as an electric motor.
This type of riding lawnmower is used to cut lawn grass to a predetermined length while a person rides on and drives the riding lawnmower. When turning, by changing the rotational speeds of traction power sources, such as two electric motors provided on both the left and right side of the vehicle, turning is executed such that the wheel corresponding to the traction power source on the side on which the rotational speed is made higher is positioned on the outside. Furthermore, the caster wheel enables free steering in which the direction thereof can freely change, and the direction thereof changes to the turning direction that is determined in accordance with the speed difference between the main drive wheels.
Further, U.S. Pat. No. 7,017,327 discloses an electrically-driven riding lawnmower comprising two steering control wheels on the front side and two drive wheels on the rear side, in which two electric motors for steering are used to make the two steering control wheels face in a predetermined direction.
Related art literature that relates to the present invention according to the third aspects includes, in addition to the above-noted U.S. Pat. No. 7,017,327, International Patent Publication No. 2006/086412, U.S. Pat. Nos. 5,794,422, 3,732,671, International Patent Publication No. 97/28681, and Japanese Patent Publication No. 2006-507789.
In a conventional riding lawnmower comprising caster wheels and main drive wheels in which the caster wheels are allowed to steer freely, there is a possibility that trouble will occur on a sloping surface. For example, as a first kind of trouble, when the operator attempts to turn the vehicle while traveling over a sloping surface, there is a possibility that a force acting on the caster wheels in a downward direction produced as a result of gravity acting on the vehicle will cause the caster wheels to have a greater downward direction than the direction to which the driver it attempting to turn. There is therefore a possibility that the driver will be unable to make the riding lawnmower accurately proceed in the desired direction. In this respect, in the case of the electrically-driven lawnmower vehicle described in U.S. Pat. No. 7,017,327, the two steering control wheels are configured to be caused to face in a predetermined direction by two electric motors for steering. However, in a case in which steering is performed by continuously orienting the two steering control wheels in response to the drive wheels, because the direction of the two steering control wheels is also determined by the electric motors during high-speed turning that would be unthinkable when traveling on a sloping surface, the size of the electric motors for steering for the steering control wheels tends to become larger. More specifically, in the case of a conventionally configured riding lawnmower, there is a disadvantage that it is difficult to accurately turn the riding lawnmower in a direction desired by the driver when traveling on a sloping surface without increasing the size of a traction power source such as an electric motor.
A second disadvantage is that, if a riding lawnmower is stopped on a sloping surface, when the driver attempts to make the vehicle start moving again by, for example, releasing each of the activated braking devices by stepping on the accelerator pedal and the parking brake that is a mechanical brake, before the vehicle starts to move forward under the power of a traction power source such as the electric motor for driving, there is the possibility that the vehicle will slip downward on the slope; even a small slip can cause the driver to feel a sense of discomfort.
A third disadvantage is that when the riding lawnmower is climbing up a sloping surface there is the possibility that the driving power will be insufficient when the driver attempts to make the riding lawnmower climb the slope with two drive wheels and the drive wheels may slip. This is undesirable because the drive wheels will damage the lawn if they slip on the surface.
A fourth disadvantage is that due to a weight transfer acting on the vehicle when a riding lawnmower is descending on a sloping surface, there is the possibility that the vehicle will tend to descend at a higher speed than the speed desired by the driver. This case is also undesirable because the lawn may be damaged, similarly to the foregoing case.
In the electrically-driven riding lawnmower disclosed in U.S. Pat. No. 7,017,327, no consideration whatsoever is given to the above-described second to fourth disadvantages. Thus, in the case of the conventionally considered riding lawnmower, there is the possibility that a disadvantage will arise when the vehicle is on a sloping surface.